1. Field of the Invention
The present invention relates to a hydraulic pump used together with an automotive power steering apparatus.
2. Description of the Prior Art
In hydraulic pumps used together with automotive power steering apparatus, since a pump rotor is rotated by an automotive engine, a flow rate of pressurized fluid discharged from a pump is increased in proportion to an increase in a rotational speed of the engine. For this reason, it has been a practice to reduce engine power loss by providing the pump with a flow volume control valve for bypassing to a low pressure zone a surplus flow volume other than a constant flow volume that a power steering apparatus consumes.
However, in these conventional pumps, when the pump rotor is rotated at a high speed as rotation of the engine is increased, a greater amount of bypass fluid is returned to the inlet port of the pump and thus cavitation has been caused in the bypass fluid, which has been the cause of reduction of pump efficiency and unpleasant noise.